These models are available with either round hatches or elongated hatches. Up until 2016 the round hatches were hinged and could be opened and closed. After that they were changed to simple/static plugs. In addition to being sold separately, these models are also available in 4-unit "Runner Packs".
The prototype for these models is American Car & Foundry's CF4650 hopper. These cars were introduced in 1963 and entered service in 1964, although the Micro-Trains model represents a later version (built starting in 1971).